Zahir Shah's return coincided with news that a US fighter plane had accidentally bombed a group of Canadian troops in Afghanistan, killing four and injuring eight of them.

The incident happened during a routine training exercise near the southern city of Kandahar.

In Kabul, a newly-trained Afghan honour guard stood to attention as the 87-year-old former monarch stepped off an Italian military plane.

Zahir Shah, a Pashtun, ruled for 40 years until he
was deposed by a cousin while on holiday in Italy in 1973.

Symbol of past

He returned as an ordinary citizen - but he may have a significant political role to play. He is widely seen as a symbol of a kinder, pre-war Afghanistan, our correspondent says.

Hamid Karzai (left) escorted Zahir Shah back from Rome

He was escorted home from Italy by Afghanistan's interim leader, Hamid Karzai, and six government ministers.

General Abdul Rashid Dostam - a powerful faction leader in the north and interim deputy defence minister - walked alongside Zahir Shah at the airport.

The former king, wearing a brown leather jacket, was kissed by tribal elders before heading off for his newly restored villa in a bullet-proof Mercedes.

Well-armed international peacekeepers and Afghan troops lined the road to the airport, backed by tanks and other armoured vehicles.

Zahir Shah has said he never intends to leave Afghanistan again.

Media silence

In a sign of political sensitivities surrounding his return, there was no announcement of it on radio or television. And there were no flags or welcoming banners in the city streets.

A bomb blast which reportedly killed three people in the southeastern town of Khost on Thursday served to heighten security concerns.

The former king still commands considerable respect

The Afghan Islamic Press agency said the blast happened in a busy market and a number of people were also injured. It was the third in the town since the fall of the Taleban regime.

The ex-king's return had been postponed several times, due to security concerns.

Last week, there was an assassination attempt on the Afghan defence minister, and early this month more than 200 people were arrested on suspicion of planning a bombing campaign against the ex-king and Mr Karzai.

Zahir Shah's family is no stranger to political violence; he came to the throne in 1933 after his father, Nadir Shah, was assassinated.

Italian security

Italian security forces, Afghan guards and the international force in Kabul are taking part in the operation to protect him.

Once home, a special detachment of 40 carabinieri will continue to protect him for several months while they train his own security personnel.

For Mr Karzai's administration, the return of Zahir Shah is a litmus test of how safe Kabul now is.

Mr Karzai said the return of the former king was a sign of peace.

"We hope his arrival brings more stability, prosperity, development and economical welfare to Afghanistan," he added.

Loya jirga

Mr Karzai, along with many ordinary Afghans and Western officials, is hopeful that Zahir Shah will act as a unifying figure for Afghanistan's many ethnic groups.

But observers say some powerful figures - including members of the Northern Alliance - are wary of his return, fearing it could provide a rallying point for their opponents.

The former monarch has been living with his family in a gated community in a Rome suburb ever since he was deposed.

He has said that he is not coming with the intention of reclaiming the throne of Afghanistan, but he is expected to open the loya jirga or grand tribal council to be convened in June.

The loya jirga, to which elections have begun, will choose an 18-month transitional government to replace Mr Karzai's interim administration.